Turbo vs. no turbo on the same engine will give you worse mileage even without getting your foot into it.
The recycling of the exhaust is used to drive a turbine to force more air into the intake. More fuel is needed to keep up with the increased air since the turbo is never off even at low rpms's.
As the former owner of both turbo and non turbo RX-7's I've been through a lot of turbo issues.
__________________ 2008 V6 Deluxe Convertible, Torch Red/Parchment top and interior, 5-speed manual, Exterior Sport Appearance Package
Mods:
K&N 63 Aircharger Cold Air Intake, JBA Evol Axle-Back Exhaust, Hurst Competition/Plus Short Throw Shifter,
Ford Racing Performance Parts front strut brace,
Ford Racing Performance Parts rear lowering springs,
GT Vert rear anti-sway bar | 
Turbo 
